Process for the production of acetylene



Filed Feb. 14, 1946 aou/A313 suona HOLVAB-IB 1351309 Patented Jan. 8, 1,952

PROCESS Foa THE PRODUCTION OF AcE'rYLENE Han-151A. butcher, Bartlesville, Okla., asslgno to Phillips Petroleum Company, a corporation of Delaware Application February 14, 1946, Serial No. 647,589

1 Claim.

the' resulting hot pebbles to a second heating or conversion chamber for heating the gases being processed and :furnishing the heat of reaction. A continuous stream of hot-pebbles is passed thru the conversion .chamber by gravity flow and transferred by means of a bucket type elevator .(or otherlifting device) to the pebble heater for reheating and recycling. .thru the system. A third chamber is sometimes placed below the conversion chamber toreceive and cool the pebbles by contact with a stream of air before being transf erred by the elevator to the pebble heating chamber. 4The air heated by the pebbles in the cooling chamber is passed to the combustion zone ofthe pebble heater to support fuel combustion and permit attainment of higher temperatures in the pebble heater than -would be possible without preheatedv air. ...While this practice of cooling the.1 pebbles in their-circulation between the conversion cham- .ber and the elevator avoids the necessity for high .temperature alloy equipment in the elevator and provides for the use of preheated air :for fuel combustion, it necessitates an extremely high differential between pebble inlet and outlet temperatures in the pebble h eater and therebyincreases fuel consumption and places a lower limit on maximum temperatures attainable therein than is obtainable by this invention. In conven- .tional procedure, there is also a lack of utilization of the large amount of sensible heat in the elliuent hydrocarbons from the conversion zone which vmaybe ata temperature of from about 1400 to `more than 3000-F. depending upon the particular process involved. .l l

It is an object of the present invention to permit lower pebble temperaturein elevator equipment, without proportionately limiting the maximum temperature obtainable in the conversion zone. A Y It is axiurther object ofl .the presenti invention 2 to provide arrangements of apparatus and proc.- esses which facilitate the utilization of the sensible heat of processed hydrocarbon gases in pebg ble-heater-type apparatus and thereby to permit the attainment of higher temperatures in the conversion zone than are .conventional in such apparatus and processes. v

Other objects and applications of the present invention will become apparent in the accom- Danying description.

In one embodiment of the invention, a pebble preheating chamber is positioned above the peb.- ble heater in a conventional pebble-heater-type apparatus and the pebbles passing therethru are preheated by contact with hot eiiluent conversion products from the conversion chamber. This procedure desirably cools the conversion products and raises the temperature of the pebbles, thereby decreasing the differential between the pebble inlet and outlet temperatures in the pebble heating chamber and making it feasible to attain pebble temperatures in the neighborhood of 3700 F.

In another embodiment of the invention the effluent products from the conversion chamberare quenched tosuch a temperature as will prevent or decrease further reactions therein before being passed thru the pebble preheating chamber. .It is found that in some cases, the quenching of the processed material in the pebble preheater'is entirely too slow to adequately prevent.. continued reactions within and between the various constituents. In .such cases, quenching of the reaction products immediately after they leave the conversion chamber by the direct injection of-water or other cooling fluid, prevents 4further reaction by lowering the temperature-without any substantial loss in sensible heat availablefor use in the pebble preheater. v v

The invention has particular application in thermal cracking and dehydrogenation processes which can be most advantageously performed at temperatures of about 20003500 F., but it also has application to processes operating in the Arange of 11002000 F. A specific application of the invention is in the cracking of light hydro'- carbons to produce ethylene at about 2000 F. in pebble heater apparatus and then passingv the hot product to a pebble heater system including a pebble preheater and a pebblecooler, thereby cracking the ethylene to acetylene at temperatures in the range of about 3000 3500 Another application ofthe invention is inthe 66 cracking of propaneat temperatures of v1800"- 3000 F. to produce a fuel gas of about '100 B. t. u. for supplementing city gas system supplies:

'I'he term pebble" as used throughout the specication denotes any refractory material in fiowable form and size which can be utilized to carry heat from one zone to another. Pebbles are conventionally substantially spherical and are about 1/8" to about 1" in diameter with the preferred size for high temperature processes about yg". Pebbles must be of refractory materials which will withstand temperatures at least as high as the highest temperature attained in the the higher .temperatures to use the best high/ temperature refractories, at least in the hottest areas of the pebble heating chamber and in the combustion furnace.

For a more complete understanding of the invention, reference may be had to the accompanying drawing in which Figure 1 is a diagrammatic showing of apparatus arranged to preheat pebbles with quenched eiliuents from the conversion zone along with preheating the feed and the air for the combustion zone.

. -Figure 2-shows diagrammatically an arrangement of apparatus showing a modification in which the pebble preheater is positioned close to the. conversion chamber permitting a short flow line therebetween and in which the air and fuel are preheated and the products are quenched .before entering the preheater.

, While the processes and apparatus f the invention are particularly applicable to the conversion of hydrocarbons, they have a Wide application to endothermic reactions generally. Such processes as the manufacture of carbon disulfide from gaseous hydrocarbons and sulfur-containing gases, and the manufacture of HCN from :ammonia and methane may advantageously be out according to the present invention. The limitation of the ensuing remarks to the production of hydrocarbons is not to be construed as a limitation of the invention to such processes.

Referring more particularly to Figures 1, 11, 12, 13 and 14 are four refractory lined chambers disposed one above the other, each communicating with the one below it through conduits I5. I6 and I1. Conduits I3 and I9 are outlet and inlet means for ow of pebbles out of chamber I4 and into chamber II. respectively. Star wheel 2 I, or other now-control device, conduit 22, bucket elevator 23,. and conduit 24 complete the pebble fiowcircuit. In operation pebbles are admitted to chamber Il and flow by gravity thru the other chambers in succession, each of which, along with the connecting conduits, is substantially filled with these heat-carrying pebbles of a refractory nature. The pebble flow is controlled by star wheel 2| which feeds pebbles into conduit 22 and thence into the elevator 23 which returns them io pebble preheater II via conduits 24 and I9 to complete the cycle. This technique of operation inherently results in maintaining a compact, contending from the inlet of the uppermost chamber II to the pebble how-control device 2| below the outlet of the lowermost chamber I4. A screening device in 22. not shown, separates nes and broken pebbles for 'removal thru a trap door not shown. A door in conduit 24. not shown, may be utilized to add pebbles to the system for replacement or initial operation.

In operation any desirable fuel is fed thru line 26 into burner or furnace 26 mixed with air from line 2'I and is burned to produce the desired heating of pebbles in chamber I2. Additional air requirements may be supplied thru line 28, controlled by valve 23. The hot combustion gases from burner 26 pass thru chamber I2 countercurrently to the flow of pebbles therethru and pass out of the chamber to indirect heat exchanger 32 via line 3|. The hydrocarbon feed to be converted is passed thru heatv exchanger 32 via line 3.3 into conversion chamber I3-where it is heated by hot pebbles flowing downwardly thru the chamber. Eiiiuent gases from conversion chamber I3 are quenched in line 34 by a relatively cold iiuid admitted thru line 35 which is controlled by valve 36. Valve 36 is operated by temperature recorder controller 31 which responds to temperature changes in line 34, automatically regulating the amount of quenching fluid admitted to line 34 to maintain a predetermined temperature therein. The quenched hydrocarbons in line 34 pass thru pebble preheater II in intimate contact with a stream of pebbles therein. giving up heat to the pebbles and passing to further treating apparatus via line 33.

In order to simultaneously heat air for fuel combustion in burner 26 and cool pebbles before passing them into elevator 23, air is admitted to chamber I4 via line 39 and is taken oil via line 21 which vfeeds hot air to burner 26. Lines 4I, 42. 43 and 45 supply steam to the areas between chambers in order to minimize escape of .gases from chamber to chamber.

Where it is preferred to have a short flow line for hydrocarbon eiliuents from the conversion chamber, the arrangement shown in Figure 2 is advantageous. Line 34 can be made exceedingly short to bring the hot hydrocarbons into contact with cooler pebbles in chamber I I in the shortest possible time to provide for an earlier quench. However, the gaseous products may be quenched in line 34, just as in the modification illustrated in Figure 1. by injecting cool fluid into the line thru line 35. This arrangement necessitates additional elevator equipment such as pebble outlet 6I, star valve 48, conduits 41 and 43, and bucket elevator 46 for conveying the pebbles from the outlet of pebble preheater I I to the inlet of pebble heater I2.

In the modifications shown in both Figure 1 or Figure 2, the hot eliuent combustion gas from the pebble heater may be used to preheat either the fuel or the hydrocarbon feed. In cases where a hot hydrocarbon feed is available preheatlng of the fuel is feasible. Such is the case where light hydrocarbons are cracked to produce ethylene and the hotethylene is further cracked at higher temperatures to produce acetylene. The hot ethylene can be fed into chamber I3 without any further preheating allowing opportunity to preheat the fuel ,by indirect heat exchange with eiliuent combustion gas.

The apparatus and processes of the inventio permit much flexibility as to operating conditions. The rate of pebble flow thru the system can readily be adjusted and correlated with the difassegno temperature in the reaction .zone maybe varied from about l100 to 3500""F.l by controlling the rate of flow of pebbles, the amount of. preheating of. fuel, feed, andl combustion air, and the amount of4 fuel' consumed in the burner attached tothe .pebblelheaten Pebbles will vary in temperature, as they leave the pebble heater, from about 1500 to wellabove 3500 F. and will be cooled to a temperature within the range of about 800 to 2000" F. as they leave the conversion zone. Pebble outletv temperature in the air heater will vary from about 500 to 900 F. depending upon the entering temperature and the amount of heating of air taking place. It is found that air may be heated to temperatures of about 500 to 1000 and'that adequate supplies `of air may be preheated within this range.

Eflluents from the conversion zone will not always require quenching and may be cycled thru the pebble preheater to be quenched by contact with cooler pebbles therein. In most cases, however, itis desirable, and highly essential in others', that the hot hydrocarbons leaving the conversion zone be immediately quenched to within the range of about 900i4 to 1400 F.' Since pebbles admitted to the -preheater are at atemperature of about 450 to 850 F. they can be preheated with the eilluent hydrocarbons to, a temperature within the range of about '700 to l200 F.

Combustion gases passing thru the indirect heat exchanger are in the range of about 900 to 1500 F., depending upon the temperature maintained in the pebble heater (combustion zone) and the rate of flow of pebbles therethru. With this available source of heat, either feed or fuel gases may be heated to temperatures within the range of about 500 to 1050 F.

Various pressures from subatmospheric to superatmospheric may be used in the apparatus but only small variations in pressures from zone to zone, e. g., 2 or 3 p. s. i., are practicable. It is preferred to operate at or near atmospheric pressure.

As an illustration of the invention, when about 30 mols per hour of propane are cracked at a temperature of about 2500 F. to produce a domestic fuel gas by passing propane thru a pebble heater arrangement similar to that of Figure 1, in contact with 1A" dense alumina pebbles. the following operating conditions obtain:

Pebble heater Pebble inlet temperature F 1145 Pebble outlet temperature F. 3010 Flue gas outlet temperature F 1515 Pebble circulation, pounds per hour 5120 Conversion chamber F. Pebble inlet temperature 2995 Pebble outlet temperature 1505 Feed inlet temperature 900 Product outlet temperature 2495 Temperature after water quench 1300 Air heater. n11, Pebble inlet temperature 1500 Pebble outlet temperature 695 Air inlet temperature e 100 Air outlet temperature 985 Pebble preheater uw. Pebble inlet temperature 645 Pbble'ou'tlet temperature 4 1155 ProductLi-steam inlet temperature 1295 Product-l-steam outlet temprature-. '700 From theabove data vsome of the advantages ofthe invention .can readily be seen. In'ordcr to maintain a high conversion temperature and sharp heating in thev conversion zone. it is essen tial to heat the pebbles to a high temperature and f low them thru this zone at a relatively rapid rate which results in a fairly high pebble outlet temperature. It is not feasible to handle pebbles at such temperatures (1500"v F.) in an elevator using ordinary cast iron buckets. Even handling pebbles at 1000F. requires such heavy equipment as to considerably increase the cost of hanf dling. With lower pebble temperatures, elevator equipment can be much lighter and made of considerably cheaper materials. By utilizing the air heater, lower pebble temperature without any substantial heat loss in the process is-possible. Preheating aix' for combustion partially compensates for lowering pebble temperature in the air heater. By preheating the pebbles coming from the elevator with the hot product gases, it is pos-- sible to additionally compensate for lowering the pebble temperature prior to handling in the elevator. It is by introducing pebbles into the peb-f ble heating zone at this higher temperature that, when coupled with preheatlng of the air, feed, and/or fuel, extremely high temperatures and very sharp heating in the conversion zone may be obtained. 'I'his invention makes it possible not only to attain considerably higher temperatures than are possible in conventionalapparatus by conventional procedures, but makes possible much sharper heating-at any given temperature, both of which advantages are extremely important in pebble heater apparatus and many processes performed therein.

I claim:

A continuous process for cracking a propanerich light hydrocarbon stream to produce ethylene and acetylene which comprises cracking said hydrocarbon stream in a rst cracking zone m contact with a gravitating compact stream of hot pebbles at a temperature of approximately 2000 F. so as to produce an ethylene-rich stream; heating a second gravitating compact stream of pebbles in a pebble heating zone to a temperature above 3000* F.; gravitating said second stream of hot pebbles directly from said heating zone through a second cracking zone passing the hot ethylene-rich stream at substantially eilluent temperature directly from said tlrst cracking zone in contact with said second stream of pebbles in said second cracking zone so as to crack said ethylenerich stream to an acetylene-rich stream, thereby increasing theyield of acetylene by reducing decomposition thereof effected by extended reaction time at elevated temperatures; immediately rapidly water-quenching said acetylene-rich stream to a temperature in the range of 900 to 1400 F.; passing the quenched acetylene-rich stream through a pebble preheating zone positioned above said pebble heating zone in direct heatexchange with said second pebble stream up, stream of said pebble heating zone so as to turther quench said acetylene-rich stream and preheat said pebbles; gravitating said second pebble stream from said second cracking zone through a pebble cooling zone inf contact with a .stream o! air so as to cool said pebbles to a. temperature below 900 F. and heat said air; passing at least a portion of said air to said pebble heating zone in admixture with fuel under combustion condi- 1g tions so as to heat the pebbles therein; recycling the pebbles from said pebble cooling zone to said pebble preheating zone; and recovering the acetylen'e-rich eiiluent from said preheating zone.

assumons crrm The following references are of record :in the ille oi this patent:

HARRIS A. DUTCHER. 1|

Simpson et al. Sept. '1, i948 

